Messages in this thread | | | Subject | Re: lockdep: possible reason: unannotated irqs-off. (was: Re: Linux 2.6.38-rc4) | From | Peter Zijlstra <> | Date | Tue, 08 Feb 2011 11:41:52 +0100 |
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On Tue, 2011-02-08 at 11:17 +0100, Borislav Petkov wrote: > > So, I'm getting the warning below early in the boot process. And yes, I > didn't have it on -rc3. 2.6.38-rc4-00001-g1e554e3-dirty means a debug > diff ontop of -rc4 which shouldn't have anything to do with this splat > since all it does is a couple of printk's due to -rc3 not suspending to > disk properly in some cases. > > Now, I'm not going to even pretend to understand the code but here's > what I can read out, you tell me whether it makes sense. > > spawn_ksoftirqd() is one of the early initcalls that gets called and > it's notifier callback does kthread_bind() and you can follow in the > backtrace below that this thing comes down to del_timer_sync() which > does the lockdep annotation. Now, problem as I see it, is that hardirqs > were disabled when we were called although it doesn't say so in the > irqtrace events dump after the calltrace: "hardirqs last enabled at > (999)" and our irq event stamp is 1000. > > There are actually at least three del_timer_sync()'s inflight so the > problem could be there somewhere, I dunno. > > So, is it a wrong lockdep annotation or is it a real problem? I've > attached dmesg and config.
Argh! Its an annotation nightmare that.. it didn't trigger for me when running that because I didn't have DEBUG_LOCKDEP=y.
OK, let me try and come up with another way to annotate this del_timer_sync() muck, the trouble is we want that lock to be called with BH disabled, but simply doing local_bh_disable()/local_bh_enable() has the nasty side effect of calling __do_softirq(). Faking IRQ state will trip this check_flags() debug muck..
We used to have local_irq_disable()/local_irq_enable() around it, but then people wanted to use del_timer_sync() from softirq context..
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